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  1. Thanks so much. Turns out the specific issue was that in trying to create an NPN phase splitter to test out the diff Amp, he had ONLY caps on the collector and emitter of the phase splitter. These in turn were connected to the respective bases of the two NPN transistors of the diff Amp. When he hung the channel 1 scope probe on either of the outputs of the phase splitter, the diff Amp output on channel two "worked", or at least he got an output signal that matched the sine wave input. When he disconnected the scope probe from the output of the phase splitter, the circuit essentially
  2. My son is doing an NPN transistor type diff gain circuit/CMRR breadboard for his class. He's using the +3V and -3V supplies and the AWG from the openscope MZ board. Seems to me he needs to ground the scope 1- and 2- leads to the black GND, otherwise floating, hence wacky results. He has in fact been floating these "-" leads and indeed got some weird results. Since he is using positive and negative supplies, the breadboard has no GND connection explicitly. So the path to ground is maybe thru the supplies, or some weird high impedance AC path thru the scope "+" leads. Should